Resnatron with separate retarding field



g- 21, 1955 M. GARBUNY ET AL RESNATRON WITH SEPARATE RETARDING FIELDFiled April 11, 1951 Moon/Z 472w United States Patent RESNATRON wrrnSEPARATE RETARDING FIELD Max Garbuny, Pittsburgh, and Glenn E. Sheppard,Wilkinsburg, Pa., assignors to Westinghouse Electric Cor poration, EastPittsburgh, Pa., a corporation of Pennsylvania Application April 11,1951, Serial No. 220,488

4 Claims. (Cl. 315-6) This invention relates to an electronic tube forultra high frequencies and has particular relation to an electronic tubeof the resnatron type such as described in our companion applicationSerial No. 206,744, filed January 19, 1951.

Said companion application explains the general construction anddesirable characteristics of both prior art and our improved resnatrons,pertinent hereto but not deemed necessary to repeat in full herein. Thepresent invention distinguishes from the said companion applicationessentially in the repeller construction and assembly in the resnatronand introduces desirable differences and improvements thereover.

The present invention accordingly is directed to improved construct-ionand operation of the anode of a resnatron supplemental to the desiderataset forth in said companion application.

Referring to the accompanying drawing, in which like numerals ofreference indicate similar parts in both figures thereof:

Fig. 1 is a longitudinal sectional view of a resnatron corresponding tothe more detailed showing of said companion application and illustratingthe improved repeller construction and assembly; and

Fig. 2 is a similar longitudinal sectional view of that portion of aresnatron which difiers from Fig. l, and showing a modified repeller,repeller housing and screen grid and cooling arrangement for the screengrid.

in the specific embodiment of the invention illustrated in said drawing,and referring more especially to Fig. 1, we show an envelope fabricatedas a body of revolution about an axis and made as two metallic outercylinders or body sections 10, 10 arranged endwise toward each other andupon an axis common to both. The ends facing toward each other of saidbody sections are held in proximity to, but with insulative spacing fromeach other, by a glass or other endless band insulator 11 lapping saidends and sealed to metal collars 12 the far margins of each of which aresoldered or otherwise secured vacuum-tight to annular flanges 12bencircling and sealed to the outside cylindrical surfaces of the bodysections proximate to the facing ends of said sections. The outer or farends of the cylinders or body sections 10 are sealed by metallic orother headers 13, 13'. Carried by, sealed to and projecting inwardly ofthe cylinders from said headers are coaxial inner metallic cylinders 14,14 which extend from their respective headers toward each other, butwith greater spacing between the approaching ends thereof than betweenthe proximate ends of the outer cylinders.

The chambers Within the outer cylinders around and beyond the innercylinders toward their proximate ends are arranged to constitute cavityresonators, of which one will be herein designated the anode resonator15 and the other designated the cathode resonator 16 for purpose ofdistinguishing therebetween. The proximate ends of the two cavityresonators have end Walls parallel to and adjacent each other withsufiicient spacing for insulative purposes. The end wall 17 of the anoderesonator is ice supply and discharge of a cooling medium, such aswater,

for said wall. Said end wall 17, has, at its center, a hole or passage20 therethrough disposed axially of the outer cylinder and opposite theend of the inner cylinder. A formaninous or other member 21 is locatedacross said hole or passage as a fixed part of said anode resonator endWall. Said end Wall, with its hole and foraminous member, accordinglyhas a structure constituting it both a screen grid and an anode, as wellas an end wall for the resonator.

The other chamber, above described as the cathode resonator 16, has anend wall 22 at the center of which is a hole or passage 23 ofcorresponding size to and aligned with hole or passage 20 of the screengrid or anode resonator end wall 17. It will be observed that this endwall 22, as Well as above-described end wall 17 of the anode resonator,and both passages 20 and 23 through said walls, and gap 24 between saidwalls, are all within the evacuated interior of the tube or device.

An indirectly or directly heated cathode 25 is provided within cathoderesonator 16 in axial alignment with and close proximity to the hole orpassage 23 in end wall 22. Said cathode is carried at the inner end of ahollow core 2d located coaxially within the resonator inner cylinder 14.The cathode is electrically connected to said core which accordinglyconstitutes a lead-in as well as a support for the cathode. The outerend of the core is seated in and soldered to an end plate 27 with avacuum-tight joint and the plate is supported at the exterior of header13 by a glass or other insulative cylindrical band 28 sealed at itsedges to oppositely projecting collars 29 respectively solderedvacuum-tight to the outwardly directed rim of innercylinder 1d and tothe inwardly directed face of the end plate 27. Lead-in wires 30 for thecathode heater are introduced into the said core through the end plate27 and with the aid of an appropriate seal 31.

An electron repelling electrode, herein referred to as repeller 32 isprovided within the anode resonator and, as shown, within the innercylinder 14' in said resonator. To accommodate said repeller within theinner cylinder 14', said cylinder may have a greater diameter thanrequired for and provided with the inner cylinder 14 of the cathoderesonator 16. Furthermore, the end of said inner cylinder 14' of theanode resonator toward and in proximity to the screen grid 17 isprovided with a partial closure or transverse grid termination 14parallel to said screen grid. Electrons from the cathode may accordinglyapproach the repeller, but the metallic enclosure provided by innercylinder 14 and the closure 14 shields or protects the repeller almostentirely from the radio frequency field and confines the direct currentrepeller field of the repeller within the said enclosure.

Said repeller 32 is shown convex or centrally bulging toward the screengrid-anode and is shown supported from its concave side by a lead-inpost 33 located coaxially within the anode resonator inner cylinder 14'.The remote end of said post from the repeller is sealed through theheader 1 for purposes of support and external electrical circuitconnections. The specific constniction here shown for the inner cylinderclosure portion of said header 13' comprises a metallic disc 34 solderedor otherwise secured vacuum-tight to the said lead-in post, the outerperiphery of said disc being sealed in a glass dome 35 the basal marginof which is in turn sealed to a metallic flange 36 soldered or otherwisesecured vacuum-tight to the upper end of the anode resonator.

It may be here noted that by enclosing said repeller within the innercylinder, no chokes are required for the lead-in post. However, cathodecore 26 is provided with a. choke 37 to prevent leakage of highfrequency power from the cathode resonator through seal 28 into outerspace. This choke is constructed in accordance with usual practice aquarter wave-length in dimension from a closed to an open end and withthe open end directed outwardly, thereby presenting an effect of shortcircuit at the closed end of the choke across the gap between theresonator inner cylinder and said core.

Both resonators are tunable, for which purpose each is conventionallyshown as provided with an annular piston 38 in the annular space betweenthe outer and inner cylinders 10 and 14 and 1t) and 14. These pistonsare each carried from and slidably mounted by a plurality of rods 40parallel to the cylinder axis and projecting through the header 13. Asuitable bellows 40a or other vacuum-retaining seal is provided betweeneach rod and the header, permitting necessary sliding of the rod in theheader and cylinder for tuning purposes and yet maintaining avacuum-tight condition between the rod and header.

A coaxial line 41 terminating as a loop 42 is introduced into thecathode resonator and constitutes a radio frequency input from asuitable source which may conveniently be a feed-back of a part of theradio frequency energy produced in the anode resonator. The anoderesonator is also shown equipped with a coaxial line 43 terminating as aloop 44 in said resonator and constituting a radio frequency output.Both coaxial lines 41 and 43 are constructed to be vacuum-tight so as tomaintain the vacuum in said resonators.

Appropriate direct current potentials are applied to the repeller,cathode and screen grid-anode, and according to the present showing,separate sources 45, 46 and 47 respectively are here depicted, although,as in the companion application above-mentioned, suitable tapping from asingle source may be arranged. The repeller may also be connected, asthrough transformer 48 with a desired source of modulation for uses andpurposes more fully explained in said companion application.

The potentials applied to the several electrodes are proportioned tocause a copious flow of electrons from the cathode to proximity of therepeller and reflection from the repeller back to the screen grid-anode.Divergence of the electrons in the reflected path is desirable so thatthe non-foraminous part of the screen grid in its function as anode willintercept the electrons. Such divergence is obtained by virtue of theconvex surface of the repeller and is permitted by virtue of the gridtermination 14" having an open work area considerably greater indiameter than the foraminous area of the screen grid 21.

Referring now to Fig. 2, it may first be said that the parts broken awayand not shown would be, if shown, exact duplicates of the correspondingparts of Fig. 1. A pair of tunable resonators each having outer andinner metallic cylinders and input and output connections areaccordingly to be understood as included in both showings.

In Fig. 2, the metallic end wall 17a of the anode resonator 15 is shownhollow so as to provide a cooling chamber 18a therein to which pipes 19are connected for supply and discharge of a cooling medium. Said endwall 17a has, at its center, a frusto-conical hole or passage 200therethrough disposed axially of the outer cylinder 10 and with thelarger end or flare of said passage directed away from the cathode. Thesmaller end of the said passage toward the cathode is provided with aforaminous member or grid 21a as a fixed part of the end wall structure.As in Fig. 1, said end wall 17a with its frusto-conical passage andforaminous member 21:: constitutes in part both an anode and a screengrid as well as, in its entirety, an end wall for the resonator.

Inner cylinder 14a in anode resonator 15 has a partial closure or gridtermination 14b at its end next the screen grid and said termination isfrusto-conical and coaxial with, but spaced inwardly from, thefrusto-conical passage wall of said screen grid 21a. The small end ofthe frusto-conical termination 14b is perforate for admitting electronstherein from the cathode, and the flaring wall of said termination is ofopen-work or grid construction to permit outflow of electronstherethrough to the frustoconical passage wall of the screen grid-anode.Two parallel ribs 60, 60 are shown on the face of the frustoconicalpassage wall spaced apart in approximate juxtaposition to the limits ofthe perforate area of the inner tube termination. The surface of thepassage wall between said ribs constitutes a collector or anode 61 forthe. electrons and, obviously from the drawing, is disposedadvantageously with respect to the cooling medium.

All electron repelling electrode, herein referred to as repeller 32a isprovided within the inner cylinder and frusto-conical termination ofsaid cylinder with the same advantages as described in connection withFig. 1. Said repeller in this instance is conical and coaxial with thefrusto-conical termination of the inner cylinder. The larger end of theconical repeller is directed toward the far end of the resonator and ismounted on and carried by lead-in post 33. With potentials applied, aswill be understood from the foregoing description and from saidcompanion application, electrons are reflected and in their reflectedpaths flow away from the repeller perpendicular to the nearest portionof the repeller surface or radially outward from the cone repeller tothe collector or anode surface. In this construction, as with Fig. 1,interference is substantially avoided between the radio frequency fieldand the direct current repeller field.

The'herein described reflex resnatron allows a density modulated beam ofelectrons to enter first the anode resonator then the repeller chamberwhere it encounters the reflecting direct current repeller field, and isreflected. On the way to and from the repeller field the beam traversesan opposing radio frequency field to which the beam surrenders kineticenergy. In the companion application above mentioned, the conversionefliciency depends strongly on the value of the retarding anode orreflector field because of the timing criterion, hence the devicethereof provides self-modulation with small power of the modulatorsource 48. The simplicity of that device entails also certain rigorousconstructional requirements; for instance, the superpositioning ofretarding direct current and radio frequency fields in the output gapmakes changes in the geometry effective for both fields in the same way.An example is that a change of s'creen-to-anode distance of that deviceto accommodate various values of the screen accelerating voltage (forchanges of power level) also changes the tuning of the output cavity.

This drawback is avoided in the presently disclosed invention, gaining,also, certain other advantages. The tube of this invention, likeresnatrons of the prior art, when used as an amplifier, has its electronbeam first density modulated in the cathode-grid resonator 16 by anexternal driver or oscillator, or, when used as an oscillator, has itselectron beam density modulated by feedback from the anode-gridresonator 15. The density modulated and preferably beam-formed electronstream passes an accelerating screen of relatively high potential toenter an output cavity or resonator 15 tuned to resonator 16. Usually inresnatrons, the anode is available to the electrons by direct flow ofthe electrons thereto, but in the present invention the electronsentering resonator 15 find a further grid or the like, 14a or 14b,which, with inner cylinder 14, substantially separates the radiofrequency space from the retarding field of a repeller from which theyare reflected toward the anode-screen. Thus the electrons traverse aradio frequency field first, that field being relatively free of adirect current component, and the electrons give up some energy to thatfield.

Next the electrons enter the inner or repeller chamber Where theyencounter the segregated retarding direct ourrent essentially staticfield of the repeller and thereby are reflected into the radio frequencyspace of resonator 15. During transit of the electrons in theirreflected path in the resonator, radio frequency field polarity againopposes motion of the electrons and further energy is derived by theresonator from the electrons. The degree to which this is the case isdetermined by the modulating voltage on the reflecting electrode orrepeller and the modulation in turn determines the instantaneous valueof efliciency and output power level.

The device of the present disclosure has most of the advantages of ourpreviously disclosed reflex resnatron. However, at the expense of anadditional grid as herein described, the present invention offersadditional features and advantages, some of which may be explained asfollows:

(1) The invention attains a wide band width in use. The feature of widebandwidth can be understood in the following way: Up to, and includingthe third grid, the device represents in all aspects the case of aconventional resnatron with plate and screen on the same direct currentpotential. If a certain power level P is maintained in the outputcavity, a given loaded shunt impedance R1 will produce a radio frequencygap voltage V, given by In the conventional resnatron R1 is so adjustedthat ideally electrons coming from the screen with an energy V1 are justdecelerated to speed zero, or substantially so, when they arrive at theplate, i. c., they have surrendered all their energy to the field. Inthe case of the disclosed device, however, one will choose underotherwise identical values of power and screen voltage V1 a loaded shuntresistance so that only half of the opposing radio frequency voltage iscreated. The electrons arnive then at the third grid, by way of examplewith one half of their initial energy eV1, make a return trip in theretarding field and (with correctly adjusted transit time conditions)yield the second half or other balance of their energy on their way backto the screen-anode. The same considerations hold for electrons which,because of modulating or entrance phase conditions, do not yield alltheir energy. We have shown therefore that under otherwise identicalconditions, the described device allows one quarter the usual loadedshunt resistance. This means in turn that, other things being equal, areduction of the ideally loaded Q by a factor 4 is allowed, or thatfour-fold bandwidth is obtained over the conventional resnatron. Thisadvantage is a direct result of the separation of retarding radiofrequency and direct current fields, since the electrons have totraverse the entire length of the radio frequency field. The reflexresnatron, as described in our said companion application, allows theelectrons to go only part of the way in the combined radio frequency anddirect curernt field, so that a larger radio frequency voltage isnecessary for opposition, necessitating a larger shunt resistance. Theadvantage is in part given away, whereas it is fully used in thisdevice. In addition, it should be remembered that the input cavity isallowed to have very high Q, without affecting the bandwith of thismodulating scheme.

(2) Flexible voltage adjustment is accomplished by the presentinvention. The resonance condition between the reflected beam transittimes and the phase of the radio frequency field introduces thecondition that for larger screen voltages the reflecting plate mustrecede from the screen. This can now be done without changing the tuningof the output cavity, since the latter is essentially isolated.

(3) This invention gains a desirable result of dispensing with chokesfor the anode lead. The separation of repeller field and radio frequencyspace has the further advantage that no chokes are needed to insuredirect current insulation of the plate without power leakage. Chokes areinconvenient because of the necessity of flexible design and becausethey introduce an additional load with respect to the modulating system.

(4) Higher etficiency is one of the important advantages of the presentinvention. The additional parameter gained in this device can beutilized to velocity modulate the density modulated beam. Thusovermodulation can effectively increase the efiiciency of the operation.

We claim:

1. A resnatron comprising a cathode and a repeller opposite each otherfor direct flow of electrons from the cathode to the repeller, aresonator having a peripheral Wall entirely beyond the cathode andsurrounding said repeller and having an end wall also entirely beyondsaid cathode, said end wall 'having a grid in the path of direct flow ofelectrons from the cathode to the repeller, an enclosure for saidrepeller surrounded by said resonator said enclosure having passageopenings for electrons following said path of direct flow from thecathode to the repeller and having passage openings for electronsreflected from the repeller on a path other than said path of directflow from cathode to repeller.

2. A resnatron comprising a cathode resonator and an anode resonator, ascreen grid between said resonators, a cathode in the cathode resonator,and a repeller surrounded by said anode resonator, said screen gridhaving passage for electrons on a path of direct flow from the cathodeto the repeller, means for substantially segregating the direct currentfield of the repeller from the radio frequency field of the anoderesonator, said means having grill openings for passing electronsreflected from the repeller, and said screen grid having an anodesurface area imperforate to electron passage for receiving electronsreflected by said repeller, said area being beyond the cathode resonatorand within the anode resonator.

3. A resnatron comprising a cathode resonator and an anode resonator, ascreen grid between said resonators, a cathode in the cathode resonator,and a repeller surrounded by said anode resonator, said screen gridhaving passage for electrons on a path of direct flow from the cathodeto the repeller, means for substantially segregating the direct currentfield of the repeller from the radio frequency field of the anoderesonator, said means having grill openings for passing electronsreflected from the repeller, and said screen grid having an anodesurface area imperforate to electron passage for receiving electronsreflected by said repeller, and having cooling means for said surfacearea of the screen grid.

4. A resnatron comprising a cathode and a repeller opposite each otherfor direct flow of electrons from the cathode to the repeller, aresonator having a peripheral wall entirely beyond the cathode andsurrounding said repeller and having an end wall also entirely beyondsaid cathode, said end wall having a screen grid providing passageopenings in direct line of electron flow from the cathode to therepeller and providing a non-formainous area out of direct line ofelectron flow from cathode to repeller, said repeller having means forreflecting electrons toward said non-foraminous area of said screengrid, an enclosure for said repeller, said enclosure having gridopenings for receiving electrons on said direct line of electron flowand for passing reflected electrons by a different path to saidnon-foraminous area of said screen grid.

References Cited in the file of this patent UNITED STATES PATENTS2,411,913 Pierce et al. Dec. 3, 1946 2,429,243 Snow et al. Oct. 21, 19472,468,152 Woodyard Apr. 26, 1949 2,482,769 Harrison Sept. 27, 1949

